Impact tool

ABSTRACT

An improved anvil for an impact tool is described which is especially suitable for use in a percussive tool which utilizes a hammer and anvil, both of which are surrounded by an oil bath. The anvil has a blind center hole which is vented in such a fashion so as to reduce cavitation damage at the contacting surfaces of the hammer and anvil.

United States Patent Inventors Donald N. Sullivan Lakewood, Colo.; Gregory A. Farrell, New York, N X. Appl. No. 804,168 Filed Mar. 4, 1969 Patented Feb. 2, 1971 Assignee General Dynamics Corporation a corporation of Delaware IMPACT TOOL 8 Claims, 3 Drawing Figs.

0.8. CI 173/128 Int. Cl 7. E2 1c 2/04, B25d 17/02 Field of Search 173/76, 80, l28-134 [56] References Cited UNITED STATES PATENTS l,l58,839 ll/l9l5 Pierce l l73/l3lX l,804,066 5/ 193 l Smith l 73/ 80X 2,904,964 9/1959 Kupka.... 173/1 34X 3,371,726 3/1968 Bouyoucos 173/l34 Primary Examiner-Emest R. Purser AttorneyMartin Lu Kacher ABSTRACT: An improved anvil for an impact, tool is described which is especially suitable for use in'a percussive tool which utilizes a hammer and anvil, both of which are surrounded by an 'oil bath. The anvil has a blind center hole which is vented in such a fashion so as to reduce cavitation damage at the contacting surfaces of the hammer and anvil.

PATENTED FEB 2 |97| INVENTORS.

GREGORYA. FARRELL BY DONALD IV SULLIVAN ATTORNEY 2 2 4. 9 m 1% \P g v m 6 k IMPACT TOOL ble for earth boring, pile driving and other applications.

Past impact tools have utilized a hammer element that impacts an anvil to couple energy to a load. It may be desireable to dispose the hammer and anvil in a liquid filled cavity such as that of the hydroacoustic impact tool described in US. Pat. No. 3,371,726, issued Mar. 5, 1968 to .I. V. Bouyoucos. It is in such an impact tool for which the invention is especially suitable.

Cavitation may occur at the boundary between the hammer and anvil surfaces where impact occurs. It is believed that when the hammer withdraws from the anvil, the pressure is quickly reduced and bubbles are formed at the boundary. After a short period of time, each bubble collapses as its surrounding liquid rushes towards the center of the bubble and impinges upon the impact surfaces with an explosive force. This cavitation phenomenon causes a rapid erosion of the impact surfaces, especially on the anvil. Moreover, cavitation lowers the efficiency of the impact tool and causes the other disadvantages such as noise and excessive vibration.

It is an object of the present invention to provide an improved anvil structure for impact tools which will substantially reduce cavitation.

In accordance with the present invention, there is provided an anvil structure formed with a blind center hole. The hole is vented by one or more passages so as to be in communication with the region surrounding the impact surfaces of the hammer and anvil. As the hammer withdraws from the anvil after impact, a ready source of fluid is made available to the area between the impact surfaces where the cavitation bubbles would normally be fon'ned and the withdrawing hammer quickly draws fluid into this area, thereby preventing cavitation. Preferably, the combined cross-sectional area of the venting passages should be approximately equal to the crosssectional areas of the center hole.

The invention itself, both as to its organization and method of operation, as well as additional objects and advantages thereof, will become more readily apparent from a reading of the accompanying drawings in which:

FIGS. 1, 2 and 3 are fragmentary sectional views of an impact tool showing the positions of a hammer and anvil before,

during and after impact, respectively.

Turning now to the drawings, an impact tool of the type described in the above-mentioned patent is shown. A housing 6 of the tool defines a cavity or bath 8 which is filled with hydraulic oil. The housing has a section 9 which extends into the cavity and provides a bearing for an anvil 12. The tool is also provided with a hammer 10 having an impact surface 24 opposed to the impact surface 16 of the anvil 12. The oil in the cavity 8 is in the area between the impact surfaces 16 and 24. Reference may be had to the above-mentioned patent for a description of the manner in which the hammer 10 may be driven for repetitively impacting the anvil 12.

The anvil 12 has a basic cylindrical configuration and is provided with a blind axial hole 14 which extends from its impact surface 16 directly to a position where it finally terminates in an end section 18. The hole 14 is disposed in the center poring passages 22 which extend from the bottom section 18 downwardly and outwardly to the anvil 12, thus providing communication from the hole to the outside oil bath 8. Preferably, the combined cross-sectional area of the venting passages should be approximately equal to the cross-sectional area of the center hole which prevents turbulence in order that optimum venting can be achieved. Attention should now be focused on the operation illustion of the anvil where cavitation bubbles would normally be expected to grow; namely, right along the centerline axis of symmetry 19 of the impact tool, as shown in FIG. I. At the lower end of the hole 14 there is provided a plurality of venttrated of the impact tool. In FIG. 1, the hammer is shown being driven downwardly with the oil between the surface 16 of the anvil and the impact surface 24 of the hammer being diverted in the direction shown by the arrows. At impact, a relatively static condition momentarily occurs as shown in FIG. 2 although there may be some turbulence within the cavity. Thereafter, as shown in FIG. 3, when the hammer l0 withdraws, oil is drawn from the area surrounding the anvil and up through the venting passages 22 through the hole 14 to the increasing area between the diverging surfaces 16 and 24.

The blind center hole 14 short circuits the tensile stresses in the fluid that would otherwise grow as the hammer and anvil recede, thereby minimizing cavitation. In addition, if cavitation should occur between and along the axis of symmetry of the parts, the hole will reduce the damaging effects thereof by eliminating a solid surface at the focal region which normally would be subject to cavitation.

While an embodiment of the invention has been described, variations thereof and modifications therein within the spirit of the invention will undoubtedly suggest themselves to those skilled in the art. Accordingly, the foregoing description should be taken as illustrative and not in any limiting sense.

We claim:

1. In an impact tool having anvil and hammer members disposed in a region adapted to continuously be filled with a fluid, said members having opposed impact surfaces, which are contained in a region such that said opposed impact surfaces produce cavitation as a result of their impact, the improvement which comprises:

a. a blind central hole extending from the impact surfaces of one of said members; and

b. at least one venting passage in said one member continuously communicating said region and said hole so as to substantially reduce cavitation as the hammer withdraws from the anvil after impact between said impact surfaces by permitting fluid to be drawn into the area between said members where cavitation would otherwise occur.

2. The invention as set forth in claim 1 wherein said one member is said anvil.

3. The invention as set forth in claim 2 wherein one end of said venting passage tenninates at the blind end of the said hole.

4. The invention as set forth in claim 2 wherein said hole is disposed along the centerline axis of the impact tool.

5. The invention as set forth in claim 4 wherein said passage is disposed in an acute angle to said centerline in a direction away from said anvil impact surface.

6. The invention as set forth in claim 5 wherein said anvil has a plurality of passages in communication with said hole.

7. The invention as set forth in claim 6 wherein the tool includes having a cavity in which the ends of said anvil and hammer having said impact surfaces are disposed, said fluid being located in said cavity and being hydraulic oil.

8. The invention as set forth in claim 6 wherein the combined cross-sectional area of said plurality of passages is approximately equal to the cross-sectional area of said hole. 

1. In an impact tool having anvil and hammer members disposed in a region adapted to continuously be filled with a fluid, said members having opposed impact surfaces, which are contained in a region such that said opposed impact surfaces produce cavitation as a result of their impact, the improvement which comprises: a. a blind central hole extending from the impact surfaces of one of said members; and b. at least one venting passage in said one member continuously communicating said region and said hole so as to substantially reduce cavitation as the hammer withdraws from the anvil after impact between said impact surfaces by permitting fluid to be drawn into the area between said members where cavitation would otherwise occur.
 2. The invention as set forth in claim 1 wherein said one member is said anvil.
 3. The invention as set forth in claim 2 wherein one end of said venting passage terminates at the blind end of the said hole.
 4. The invention as set forth in claim 2 wherein said hole is disposed along the centerline axis of the impact tool.
 5. The invention as set forth in claim 4 wherein said passage is disposed in an acute angle to said centerline in a direction away from said anvil impact surface.
 6. The invention as set forth in claim 5 wherein said anvil has a plurality of passages in communication with said hole.
 7. The invention as set forth in claim 6 wherein the tool includes having a cavity in which the ends of said anvil and hammer having said impact surfaces are disposed, said fluid being located in said cavity and being hydraulic oil.
 8. The invention as set forth in claim 6 wherein the combined cross-sectional area of said plurality of passages is approximatelY equal to the cross-sectional area of said hole. 